The objective of this research proposal is to determine the contribution of signal transducer and activators of transcription (STAT3 and STAT1) and mitogen activated kinases (MAPKs) in interleukin-11 (IL-11)-mediated cytoprotection in endothelial cells (ECs). IL-11 is protective in several in vivo models of immune-mediated injury and inflammation. Antibody and complement-mediated injury to donor ECs plays an important role in pathophysiology of hyperacute rejection of vascularized allografts and xenografts. Recent studies conducted by the applicant demonstrated that IL-11 protects cultured human umbilical vein ECs (HUVECs) against lysis by monoclonal anti-class I MHC antibody plus heterologous complement. Moreover, the protective action of IL- 11 is protein synthesis- dependent. IL-11 induces tyrosine phosphorylation of STAT3, STAT1, and p42 and p44, two members of MAPK family. The present proposal is designed to elucidate the role of various signaling molecule in IL-11-mediated cytoprotection. This will be accomplished using experimental designs that broaden the training and experience of the applicant. Using a retoviral transfection method, the applicant will generate stable transfectants of HUVECs that express either activatable or dominant negative forms of STAT3 (dn-STAT3) or STAT1 (dn-STAT1). Using Western blot and electrophoresis mobility shift assay (EMSA), the applicant will test whether overexpression of dn-STAT3 and dn-STAT1 effects IL-11-mediated activation of STAT3 and STAT1, respectively. Subsequently, it will be determined if overexpression of dn-STAT3 and dn-STAT1 inhibits IL-11-mediated protection against complement lysis. The activatable forms of STAT3 and STAT1 will be tested for their ability to confer (or inhibit) cytoprotection. The contribution of MAPK pathway will be assessed by using antisense to p42/p44 and c-Raf, the first enzyme in the MAPK pathway. Results from these experiment will provide insights into the intracellular signaling pathways, by which IL-11 protects against immune-mediated injury and will aid in the discovery of new therapeutic strategies for diseases associated with immune-mediated injury.